Handling, Transportation and Storage of Liquid Nitrogen
Please refer to the following documents:
- CCLRC Safety code number 2 - Safety in the handling and use of cryogenics liquid
- Liquid Nitrogen BOC - Data Safety Sheet
- SRS Safety Documentation
Table of Contents
- Properties: Liquid Nitrogen
- Known or Expected Hazards
- Operation
- Personal Protective Equipment
- Training
- Emergency Procedures
Properties: Liquid Nitrogen
- Liquid Nitrogen has a boiling point of -195.8°C
- Volume of expansion liquid to gas (at 15°C, 1 atm.) = 682.1
- Sg = 0.808 (at -195.8°C)
- Density of liquid (normal boiling point, 1 atm.) = 0.807 g/cc
- Colourless, Odourless liquid similar appearance to water
Known or Expected Hazards
a) Temperature Related- The extremely low temperature of the liquid can cause severe burn-like damage to the skin either by contact with the fluid, surfaces cooled by the fluid or evolving gases. The hazard level is greater than that of handling boiling water.
- The low temperature of the vapour can cause damage to softer tissues e.g. eyes and lungs but may not affect skin during short exposure.
- Skin can freeze and adhere to liquid nitrogen cooled surfaces causing tearing on removal.
- Soft materials e.g. rubber and plastics become brittle when cooled by liquid nitrogen and may shatter unexpectedly.
- Liquid oxygen may condense in containers of liquid nitrogen or vessels cooled by liquid nitrogen. This can be extremely hazardous because of the pressure rise on the slightest degree of warming above the boiling point of oxygen (-183°C) and the possibility of explosive reaction with oxidisable material.
- Thermal stress damage can be caused to containers because of large, rapid changes of temperature.
- Large volumes of nitrogen gas are evolved from small volumes of liquid nitrogen (approximately 700 times) and this can easily replace normal air in poorly ventilated areas leading to the danger of asphyxiation. It should be noted that oxygen normally constitutes 21% of air. Atmospheres containing less than 10% oxygen can result in brain damage and death (the gasping reflex is triggered by excess carbon dioxide and not by shortage of oxygen), levels of 18% or less are dangerous and entry into regions with levels less than 20% is not recommended.
- Oxygen condensed into leaking containers can explode on heating following resealing or blockage with ice.
Operation
- Always use liquid nitrogen in a well ventilated area, especially when filling a warm container or transfer tube or inserting a warm object, as large volumes of nitrogen gas are evolved.
- Only use containers that have been designed specifically for use with cryogenic liquids as non-specialised equipment may crack or fail. In particular, do not use food type vacuum flasks as they can implode resulting in flying glass fragments.
- Always fill warm dewars slowly to reduce temperature shock effects and to minimise splashing.
- The liquid nitrogen tap is now situated close the display area in the Outer Hall. Use it only if you have been trained to do it. When refilling for Liquid nitrogen use the onion dewar available at the station.
- DO NOT TRANSFER LIQUID NITROGEN INTO SMALL DEWARS STRAIGHT FROM THE TAP.
- Always make sure that containers of liquid nitrogen are suitably vented and unlikely to block due to ice formation.
- Beware of the formation of liquid oxygen in cold traps that are open to air or the increase of liquid oxygen content in a flask of liquid nitrogen that has been cold for a long period. (Liquid oxygen has a blue water-like appearance). However, most liquid nitrogen containers are closed except for a small neck area and the nitrogen vapour issuing from the surface forms a barrier which keeps air away from the liquid thus preventing oxygen contamination.
- Avoid skin contact with either liquid nitrogen or items cooled by liquid nitrogen as serious burns may occur.
- Always wear approved Personal Protective Equipment especially safety glasses to protect against splashes, vapour, failure of glass apparatus resulting in implosion, brittle failure of items cooled by liquid nitrogen.
- Every care and protection as identified above must be followed.
Personal Protective Equipment
- Face shield or safety glasses (provided at the station).
- Dry leather gloves even when handling equipment that has been in contact with the liquid (provided at the station).
- Lab coat or overalls are advisable to minimise skin contact, also, wear trousers over shoe/boot tops to prevent shoes filling in the event of a spillage.
Training
Users of liquid nitrogen should have received instruction in its use from their Employer. The B.O.C. leaflet “Recommended Safety Precautions for Handling Cryogenic Liquids” should be read.Emergency Procedures
Medical Emergencies |
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Medical Emergencies |
Dial 3333 on the nearest telephone and ask for the nearest First Aider. |
All incidents, whether fire or medical, should be reported to the Safety Group either directly in the case of a fire or serious injury or, in the case of a minor injury, by using the forms available around site.
